1. Field of the Invention
The present invention relates to an illuminant device, and in particular to an illuminant device with over-temperature protecting function.
2. Description of Related Art
Light emitting diodes (LEDs) have the advantages of small volume, long lifetime, difficulty damage, without mercury and lower power consumption. They are gradually replacing the fluorescent tubes and incandescent lamps and widely used in indoor or outdoor lighting and decorative lighting.
However, in comparison to other lighting source, LEDs with higher power are more prone to a problem of heat dissipation. The main reason is that the heat of the LEDs cannot be dissipated through infrared radiation. Moreover, the multiple packages of the LEDs make junction thermal resistances at different junctions such that the LEDs cannot effectively dissipate heat. In general, over-temperature operation makes the LEDs reduce light output (light attenuation), color shift and accelerate aging to shorten the lifetime of the LEDs.
In order to prevent the LED form aging, color shifting and light attenuation, the LED must prevent from operating under high temperature environment. Reference is made to FIG. 1, which is a circuit diagram of an illuminant device with high temperature cutting function. The illuminant device 10 includes an illuminant element 12, a resistor 14, and a fuse 16. The resistor 12 and the fuse 16 are respectively electrically connected to the illuminant element 12 in series. The illuminant element 12 is alternating current (AC) light emitting diode (LED). The illuminant device 10 is electrically connected to an alternating current power source ACV. The AC power source ACV provides electric power to the illuminant element 12 to light the illuminant element 12.
The fuse 16 is inexpensive, which can effectively reduce manufacturing cost. However, the fuse 16 will be damaged when operating under over high temperature and current. The fuse 16 is a disposable element, when the fuse 16 damages, the circuit includes the fuse 16 is broken because the AC power source ACV cannot conduct to the illuminant element 12, therefore the illuminant element 12 cannot be lit anymore.
Of course, users can replace a new fuse connected to the AC power source ACV and the light emitting element 12, however, the convenience of using the illuminant device 10 is reduced because the fuse 16 cannot automatic reset.
In order to solve the problem mentioned above, some manufacturers propose improved illuminant device 20 as shown in FIG. 2. The illuminant device 20 includes a base 22, a LED 24 and the thermistor 26. The LED 24 and the thermistor 26 are electrically connected to the base 22, respectively. The LED 24 and the thermistor 26 are electrically connected in series via a soldering wire 28. The resistance of the thermistor 26 is sharply increased when an operating temperature of the illuminant device 20 is higher than a predetermined value, thus preventing a power source from conducting to the LED 24.
However, the thermistor 26 and the illuminant element 24 are placed on the same lever, and the thermistor 26 is closed to the LED 24, therefore the thermistor 26 is always operating under high temperature environment, and the sensitivity of the thermistor 26 will be affected, and the thermistor 26 may be damaged. Moreover, the thermistor 26 and the LED 24 are made of semiconductor processing, when the thermistor 26 damages, the illuminant device 20 is unable to be use and user cannot fix the illuminant device 20 by itself. Furthermore, light emitted from the LED 24 is easily be blocked by the thermistor 26, and then decreases the emitting uniformity.